1. Field of the Invention
The present invention relates to a spring sheet structure which supports a coil spring used as a suspension spring.
2. Description of the Prior Art
Conventionally, coil springs have often been used as suspension springs for vehicles. The region at which this type of coil spring is disposed differs in accordance with the type of suspension. There are cases in which the coil spring is disposed separate from and independently of the shock absorber, and there are cases in which the coil spring is wound around the outer periphery of the shock absorber. Hereinafter, the latter case will be described.
A lower spring sheet is disposed at the outer peripheral portion of the cylinder of the shock absorber, and an upper spring sheet is disposed at the upper end portion of the piston rod of the shock absorber so as to oppose the lower spring sheet. A coil spring is provided between the upper spring sheet and the lower spring sheet such that the coil spring is wound around the outer peripheral portion of the shock absorber.
In this type of structure, as the coil spring extends and contracts, the end portions of the coil spring move relatively in the radial direction thereof. Due to this movement, abnormal sound is generated between the coil spring and the spring sheets, and consequently, various abnormal sound preventing measures have been taken in the conventional art. Due to the way in which the shock absorber swings, the abnormal sound is generated primarily at the lower spring sheet side, and is generated in a vicinity of a 3/4 wound portion which is the starting point at which the coil spring begins to rise spirally from the wound seat portion of the coil spring.
Hereinafter, the abnormal sound preventing structure disclosed in Japan Patent Information Organization Laid-Open No. 84-8491 will be explained. In the structure illustrated in FIG. 5, an annular concave groove 106 is formed at a predetermined position of the outer peripheral portion of a lower spring plate 104 which is welded to the outer peripheral portion of a cylinder 102 of a shock absorber 100. The lower end portion of a coil spring 108 is inserted into and engaged with the concave groove 106. Correspondingly, the annular concave groove 106 is also formed at a predetermined position of the outer peripheral portion of an upper spring sheet 110. The upper end portion of the coil spring 108 is inserted into and engaged with the concave groove 106. In accordance with this structure, the lower end portion of the coil spring 108 is held in a plane-contacting state by an inner wall 106A and an outer wall 106B of the concave groove 106. Therefore, relative radial direction movement of the lower end portion of the coil spring 108, which movement accompanies the extension and contraction of the coil spring 108, can be regulated to a certain extent.
However, in this structure, as illustrated in FIG. 6, the inner wall 106A and the outer wall 106B of the concave groove 106 have an open cross-sectional configuration in which the inner wall 106A and the outer wall 106B both open outwardly. Therefore, when the lower end portion of the coil spring 108 attempts to move in the radial direction in accordance with the extension and contraction, the lower end portion moves in the directions of the arrows in FIG. 6. Specifically, due to the lower end portion attempting to move in the radial direction in accordance with the extension and contraction of the coil spring 108, the lower end portion of the coil spring 108 slides in directions of substantially extending and contracting on the inner wall 106A and the outer wall 106B of the concave groove 106 due to the vertical component at that time. In this case, because the lower end portion of the coil spring 108 plane-contacts the inner peripheral surfaces of the inner wall 106A and the outer wall 106B of the concave groove 106, a sliding sound which accompanies movement in the directions of substantially extending and contracting becomes a relatively loud abnormal sound. Accordingly, there is room for improvement of this structure as an abnormal sound preventing structure.
The structure illustrated in FIG. 7 is a variant example disclosed in the aforementioned laid-open. Pawls 114 are formed at equal intervals by cutting the outer peripheral portion of a lower spring sheet 112 at predetermined positions. The lower end portion of a coil spring 116 is interposed and held between the pawls 114 and a lower wall 112A and a peripheral wall portion 112B of the lower spring sheet 112. Correspondingly, a plurality of the pawls 114 are formed at predetermined positions of the outer peripheral portion of an upper spring sheet 118. The upper end portion of the coil spring 116 is interposed and held between the pawls 114 and a bottom wall 118A and a peripheral wall portion 118B of the upper spring sheet 118. In accordance with this structure as well, in the same way as in the previously-described structure, radial direction movement of the lower end portion of the coil spring 116 can be regulated to a certain extent by the pawls 114 and by the bottom wall 112A and the peripheral wall portion 112B of the lower spring sheet 112.
However, in this structure as well, the pawl 114 formed at the upper left side in the drawing corresponds to a vicinity of the 3/4 wound portion of the coil spring 116. As the coil spring 116 extends and contracts, the lower end portion thereof attempts to move in the radial direction. The lower end portion thereby slides on the pawls 114 and the peripheral wall portions 112B in directions of substantially extending and contracting. Accordingly, abnormal sound is generated in the same way as in the previously-described structure.
Further, in both of these structures, in cases in which there is dispersion in coil springs, positioning cannot be effected appropriately, and the aforementioned abnormal sound is generated. Specifically, the wire diameter and the spring diameter of the coil spring are set differently for each vehicle type, and reliably positioning coil springs for all settings is not possible with the above structures. Further, even in cases in which coil springs of the same setting are used, a slight dispersion is caused due to manufacturing errors (tolerances). Therefore, in such cases as well, appropriate positioning of coil springs is not possible with the above-described structures.